Characterization of a Transcription Terminator of the Procyclin PARP A Unit of Trypanosoma brucei

The polycistronic procylcin PARP (for procyclic acidic repetitive protein) A transcription unit of Trypanosoma brucei was completely characterized by the mapping of the termination region. In addition to the tandem of procyclin genes and GRESAG 2.1, this 7.5- to 9.5-kb unit contained another gene for a putative surface protein, termed PAG (for procyclin-associated gene) 3. The terminal 3-kb sequence did not contain significant open reading frames and cross-hybridized with the beginning of one or several transcription units specific to the bloodstream form. At least three separate fragments from the terminal region were able to inhibit chloramphenicol acetyltransferase expression when inserted between either the PARP, the ribosomal, or the variable surface glycoprotein promoter and a chloramphenicol acetyltransferase reporter gene. This inhibition was due to an orientation-dependent transcription termination caused by the combination of several attenuator elements with no obvious sequence conservation. The procyclin transcription terminator appeared unable to inhibit transcription by polymerase II.